Due to environmental concerns, among other things, there has been a movement toward reducing the amount of volatile organic compounds (VOCs) in paints, stains, and other coating compositions. However, some of the desirable properties of the coating compositions had been negatively affected by the absence of VOCs in those compositions. Companies have recently been searching for formulations and methods of making coating compositions with a low VOC content, but without sacrificing the properties provided by the previous inclusion of VOCs.
Typically, additives that facilitated or caused properties, such as better film coalescence from a latex, better resistance to blocking, better physical and chemical scrub resistance, and tougher coatings, among others, were classified as volatile organic compounds, which evaporated into the environment upon film formation. The evaporation often resulted in undesirable aromas, and exposure to such fumes, particularly in areas that were not well ventilated, was a health concern. Thus, less volatile or non-volatile compounds that impart comparable (or superior) properties are needed to replace VOCs. Some of the efforts focused on decreasing the volatility of the additives. Increasing the molecular weight of the additives and changing the functionality of the additives have also been attempted.
For instance, U.S. Pat. No. 6,762,230 B2 discloses coating compositions containing a latex polymer and dispersible coalescents having a VOC content less than about 50%. The '230 patent describes the dispersible coalescents as preferably having low molecular weight, though the examples indicate their structure as being from a reaction between ε-caprolactone and an alcohol or a carboxylic acid. The '230 patent does not disclose the presence of a crosslinking agent.
Previously, latex film drying was facilitated by the presence of a crosslinking agent that would not only help physically coalesce the latex polymers but also chemically crosslink the polymer particles together, typically resulting in stronger films.
U.S. Pat. No. 6,069,200 discloses aqueous curable compositions comprising polymers with sterically hindered alkoxylated silane groups and acid groups blocked by fugitive bases. The '200 patent teaches that these groups can be crosslinked using organometallic catalysts. The compositions of the '200 patent are disclosed to be used as adhesives, sealants, and paints, and are disclosed to have improved properties including solvent resistance, adhesion, hardness, abrasion resistance, and mar resistance. The '200 patent, however, teaches the use of VOCs and does not disclose low-VOC compositions.
U.S. Patent Application Publication No. 2004/0161542 A1 discloses an aqueous composition and method for preparing a non-yellowing coating therefrom. The '542 publication discloses compositions having less than 5 wt % VOCs and discloses that the compositions are useful for preparing crosslinked coatings. The '542 publication also discloses that the polymers in the compositions contain at least one unsaturated fatty acid ester group. In addition, like the '200 patent, the '542 publication discloses crosslinking of the polymers, but through an auto-oxidative mechanism using atmospheric oxygen and the ethylenic double bond from the fatty acid ester. Furthermore, the '542 publication does not disclose some useful additives, such as open time agents.
Thus, there remains a need for low-VOC compositions for use in coatings and related applications that use alternative chemistries and that also improve certain as-applied coating properties without using many VOCs, while maintaining compositional properties and other coating properties at desirable levels.